I'm not sure they make automotive batteries that need to be maintained anymore unless they are some cheapo battery...which would explain why it won't hold a charge after only 2 years. Small engine batteries often allow for the addition of additional acid. Many batteries do have the caps still and vents, but it usually states to never remove the caps and the vent is just to get rid of excess off gassing from the continuous chemical reaction going on inside the battery.
I would suggest taking the car into a sears and get the diehard service done. They will test your current battery to see if it's still good. If not get a new one, diehard is now made by East Penn Manufacturing out of Fleetwood, PA area. On a side note, they are the number one lead recycler in the US and treat their employees well. Also, the battery warranties are hard to beat.
After they test your battery/replace it if needed they will run a starting system test as well as a charging system test to ensure the battery being dead isn't cause by a bad alternator, ground, key off drain, etc. it's $14.99 and well worth it in my opinion....Yes, I do work at a Sears Autocenter part time, but it truly is worth the time and money.